Map matching processing of acquiring an own vehicle position (for example, referred to as “map matching position”) on a road link in map data is carried out in a navigation device used for a mobile body such as a vehicle.
For example, an own vehicle position (for example, referred to as “estimated position”) and an own vehicle direction, which are calculated based on data output from a vehicle speed sensor and a gyro sensor, and map data are used in the map matching processing. Then, for example, a link having a position error between the estimated position and a candidate position on the link, and a direction error between the own vehicle direction and a link direction respectively satisfying predetermined conditions is selected as a map matching subject. Moreover, a likelihood (also referred to as “evaluation value”, “confidence”, or the like) is acquired by means of a predetermined likelihood function for each link subject to the map matching, or for a candidate position on each link, and a map matching position is acquired on a link high in the likelihood. For example, such a description that a likelihood of an own vehicle position on a road link is calculated based on an own vehicle position and an error covariance exists in Patent Literature 1.
Moreover, when a graphic (for example, referred to as “car mark”) representing a current position is displayed in the navigation device, a determination (hereinafter also referred to as “free state determination”) of whether the graphic is displayed at a position acquired by the map matching or a position acquired without the map matching is made. It should be noted that the display state with the map matching is referred to as “matching state”, and the display state without the map matching is referred to as “free state”.
A condition determination by using respective parameters of the own vehicle such as the position error, the direction error, and a GPS reception state, and thresholds for the respective parameters is made in the free state determination.